The present invention relates generally to a method for treating tar, and, more particularly to a method for separating valuable products from tar by treating the tar with steam. The present invention is particularly useful for separating valuable products from phenol tar and/or mixtures of phenol tar with bisphenol-A tar.
Phenol tar is a heavy, viscous byproduct produced in the industrial synthesis of phenol and acetone from cumene. Phenol tar is a complex mixture which comprises phenol, acetophenone, dimethylbenzyl alcohol, .alpha.-methyl styrene dimers, p-cumylphenol, small amounts of salts (principally Na.sub.2 SO.sub.4) and many other chemicals in smaller amounts. It is difficult to dispose of phenol tar in an environmentally acceptable manner. Specifically, burning phenol tar is not a good disposal solution because it contains many ingredients which do not burn readily, such as phenol and Na.sub.2 SO.sub.4. Therefore, a need exists to find more environmentally acceptable methods of disposing of phenol tar. The present invention reduces pollution resulting from the disposal of phenol tar by extracting valuable chemicals from the tar that can be recycled, thus reducing the amount of phenol tar that must be disposed of.
U.S. Pat. No. 3,850,996 (hereinafter "the '996 Patent"), describes a conventional method for disposing of phenol tar. Specifically, the '996 Patent describes a process wherein the phenol tar is thermally broken-down by heating it in a continuous operation column-type reactor (i.e., a thermocracker). The phenol tar is first fed into the middle part of the column type reactor. Upon heating, the phenol tar is refluxed, and the vapor which does not condense is led into a separation stage. The waste tar residue is removed from the bottom of the reactor. This process operates at a pressure of about 3.5 Bars, a reflux ratio of about 8, and a temperature of about 315.degree. to 325.degree. C. The composition of the phenol tar disclosed in the '996 Patent is described in Table 1 below.
TABLE 1 ______________________________________ Phenol Tar Composition Component Composition, weight % ______________________________________ Phenol 15.4 Acetophenone 9.3 Dimethylbenzyl alcohol 9.1 p-Cumylphenol 40.9 Heavy residue 25.3 ______________________________________
The vapor obtained from the process according to the '996 patent principally comprises the valuable products: cumene, phenol and .alpha.-methylstyrene. Acetophenone, another valuable product, remains almost entirely in the bottom of the reactor with the waste tar residue.
The process described in the '996 Patent has several disadvantages. Specifically, this process produces a relatively low total yield of valuable products (i.e., products which can be recycled), and a relatively high proportion of the phenol tar is converted to waste tar residue rather than to valuable products. Moreover, the success of this process is critically dependent upon the composition of the phenol tar fed into the process--the phenol tar must be concentrated in phenol, .alpha.-methylstyrene dimers, dimethylbenzyl alcohol and cumylphenol, which can decompose into valuable products such as phenol, .alpha.-methylstyrene, and cumene. The phenol tar described above in Table 1 is amenable to the process described in the '996 patent, and could theoretically yield 541 kg of valuable products per ton of phenol tar. However, a less rich phenol tar described below in Table 2, which is recited in Russian Patent No. 2,056,400, could theoretically only yield about 270 kg of valuable products per ton of phenol tar.
TABLE 2 ______________________________________ Phenol Tar Composition Component Composition, weight % ______________________________________ Light end components &lt;0.01 Cumene 0.01 AMS 0.1 Phenol 15.2 Acetophenone 22.8 AMS 8.2 CP 13.8 Heavies remainder to 100 ______________________________________
Russian Patent No. 2,056,400, discloses a process for increasing the yield of valuable products from treating phenol tar by removing 50 to 100% of the acetophenone from the waste tar residue produced in a process analogous to that described in the '996 Patent. This is accomplished by adding bisphenol tar in a concentration of from 10 to 90% to the feedstock to provide the required pH (below about 7), and by reducing the reflux ratio to between 0.5 and 2.0. This technique can increase the total yield of valuable products by an additional 100 to 150 kg per ton of phenol tar, and has successfully produced up to 425 kg of valuable products per ton of phenol tar. However, it is noted that the success of this technique is highly dependent upon the composition of the phenol tar. Specifically, the phenol tar must be rich in phenol, .alpha.-methylstyrene dimers, dimethylbenzyl alcohol and cumylphenol, which can decompose into valuable products such as phenol, .alpha.-methylstyrene, and cumene. Generally, this method is disadvantageous because it results in a relatively low yield of valuable products.
Russian Patent Application No. 95-109134 suggests treating phenol tar with phosphoric acid that is pre-heated to between 50.degree. C. and 180.degree. C. This method is capable of producing up to 550 kg of valuable products per ton of phenol tar. However, this method produces a waste tar residue in the bottom of the reactor which comprises phosphoric acid and/or polyphosphoric acids. The presence of these acids in the waste tar leads to greater ash content in the smoke of the burned waste tar, and thus produces further pollution which makes this method undesirable in most situations.